LiF/Al cathodes and the effect of LiF thickness on the device characteristics and built-in potential of polymer light-emitting diodes

We report the characteristics of a series of polymer light-emitting diodes, fabricated with LiF/Al cathodes and differing only by the thickness of the LiF interlayer (0 nm less than or equal tod less than or equal to 11 nm). Electroabsorption studies of the internal electrostatic potential give direct evidence of a sizable reduction of the cathodic barrier height brought about by the LiF films. These results also correlate with photoemission experiments [S. E. Shaheen, G. E. Jabbour, M. M. Morrell, Y. Kawabe, B. Kippelen, N. Peyghambarian, M. F. Nabor, R. Schlaf, E. A. Mash, and N. R. Armstrong, J. Appl. Phys. 84, 2324 (1998)] and with the electroluminescence performance of the diodes. (C) 2000 American Institute of Physics. [S0003-6951(00)02845-X].